1. Field of the Invention
The present invention is directed to x-ray scanners of the type through which articles are conveyed for inspection thereof by an x-ray beam.
2. Description of the Prior Art
X-ray scanners are known in the art having an x-ray source with a collimator for generating a fan-shaped x-ray beam through which an article to be inspected is moved, with radiation attenuated by the article being detected at a radiation detector on the opposite side of the conveyor. Image processing electronics are provided for constructing a visual image from the attenuated radiation signal. Scanners of this type are used, for example, to inspect baggage.
The radiation receiver may be formed by a row of individual detectors which supply the acquired values in parallel. These values correspond to the attenuated radiation intensity, and are entered in an image memory. A continuous image is then constructed for display on a monitor based on the content of the image memory.
In x-ray scanners of this type, the quality of the signals generated by the radiation detector (or receiver) is critically dependent on the exact adjustment of the fan-shaped x-ray beam. To this end, an exact geometrical configuration of the focus of the x-ray source, the collimator, and the radiation receiver is crucial. To limit the radiation dose and the scatter radiation to a minimum, a optimally thin fan beam is desired. Thus the collimator in such scanners generally has a small column width in the range of a few tenths of a milllimeter. The radiation receiver is thus irradiated by a beam which has a width of about three millimeters, in accord with the relevant geometrical conditions (the spacing between the beam focus and the collimator, and between the collimator and the radiation receiver). The components are geometrically arranged so that the effective surface of the radiation receiver and the area of the incident radiation are substantially coincident. A precise adjustment must be undertaken to achieve this result, particularly given the use of radiation receivers which are in the form of angled detector rows.
Due to the movement of the conveyor means during operation as well as due to the placement of articles thereon, and particularly given the use of scanners of this type in vehicles as a mobile x-ray scanner, the x-ray scanner is subjected to jolts and vibrations to a considerable degree. It is therefore difficult to maintain the necessary precise adjustment of the components during operation as a result of such mechanical stresses.